1. Field of the Invention
This invention relates generally to formation of a glass fiber mat using the method commonly referred to as the Modigliani method, and more particularly relates to a means and method for coating the glass fibers with binder and/or wetting agents after formation but before collecting in a mat.
2. Description of the Related Art
Fiberglass mats, which subsequently can be infiltrated with a matrix material such as a polymer resin to form a composite, are formed conventionally by different methods. One method for making fiberglass mats is described in several patents to Modigliani, U.S. Pat. Nos. 2,546,230; 2,609,320 and 2,964,439, all of which are herein incorporated by reference.
These patents disclose an apparatus in which a slowly reciprocating, melting furnace feeds molten glass through spinning orifices which discharge an array of fine, continuous glass filaments or fibers that are wrapped circumferentially around a rapidly rotating drawing drum. The melting furnace reciprocates relatively slowly in a longitudinal direction above the drum's rapidly rotating circumferential surface, thereby forming a build-up of continuous fibers oriented at acute angles with one another. During winding of the fibers on the rotating drum, a binder, such as a thermosetting resin, is applied by spraying the fibers already deposited on the drum to bind the fibers at their overlapping junctions with fibers of previously deposited layers.
After a suitable thickness of fibers has been created, the condensed mat is removed from the drum by forming a longitudinal cut through the mat parallel with the axis of the drum. The condensed mat is subsequently deposited on a conveyor belt that moves at a very slow rate. The severed condensed mat is generally rectangular in shape, and the fibers in the mat extend, due to the orientation of the rectangular mat on the conveyor, substantially completely across the width of the mat substantially perpendicular to the direction of movement of the conveyor belt.
At the exit end of the conveyor belt, a retarding roller presses the condensed mat against the conveyor belt, which is supported by an oppositely rotating support roller. The leading end of the condensed mat beyond the retarding roller is stretched or expanded longitudinally up to hundreds of times its original, condensed length. The expanding is a continuous process with the leading end being pulled longitudinally while the retarding roller/support roller structure minimizes the forward movement of the remaining length of the condensed mat.
As the mat expands longitudinally, it also expands (“fluffs”) in the direction of the mat's thickness to a consistency resembling cotton candy. And during the expansion of the mat, the fibers that are originally oriented transversely to the direction of movement are pulled longitudinally, thereby tending to rotate and reorient the fibers to a 45 degree or greater angle with respect to the longitudinal direction. During the expansion process, in which the original mat increases in length enormously and “fluffs” to a significantly greater thickness, the mat necks down to a smaller width.
After the majority of the expanding takes place, the fluffed, expanded mat is compressed in the direction of its thickness by rolling and it is heated by radiant heaters to set the thermosetting resin incorporated during the winding of the fibers on the drum. Thereafter, the stretched glass fiber mat is wound on a spool, on which it may be transported to other locations for use in various structures such as heat, thermal and sound insulation, mechanical parts formed, for example, by pultrusion or molding, and filters.
The conventional manner of placing the binder on the fibers is to spray the layer of fibers with a binder after the fibers are wound around the drum. However, this spray coats not only the layer of fibers just wound, but to some extent also further coats fibers that were wound earlier, and were coated sufficiently with binder already. Additionally, when the binder is placed on the outwardly facing sides of the fibers, enough binder must be sprayed to wet the fibers so that the contact points between fibers (on the other sides of the fibers) contain binder. This results in superfluous coating of fibers with binder, which results in unnecessary expense and potentially undesirable properties due to excessive binder.
Therefore, the need exists for a method and apparatus that applies binder and/or a wetting agent to the fibers only to the extent necessary to cause the fibers to bind to one another.